Axial Flow Blood Pump

ABSTRACT

The invention generally relates to improved medical blood pump devices, systems, and methods. For example, blood pumps may be provided that include a housing defining a blood flow path between an inlet and an outlet. A rotor may be positioned in the blood flow path. A motor stator may be driven to rotate the rotor to provide the blood flow through the pump. Axial and/or tilt stabilization components may be provided to increase an axial and/or tilt stabilization of the rotor within the blood flow path. In some embodiments, biasing forces are provided that urge the rotor toward a bearing component. The biasing force may be provided by adjusting drive signals of the motor stator. Additionally, or alternatively, one or more magnets (e.g., permanent/stator magnets) may be provided to bias the rotor in the upstream and/or downstream direction (e.g., toward a bearing (chamfer, step, conical), or the like).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. patent application Ser.No. 15/807,398 filed Nov. 8, 2017 (Allowed); which is a Continuation ofPCT/US2016/032516 filed May 13, 2016; which claims the benefit of U.S.Provisional Appln No. 62/162,205 filed May 15, 2015; the disclosures ofwhich are incorporated herein by reference in their entirety for allpurposes.

BACKGROUND

This application relates generally to mechanical circulatory supportsystems, and more specifically relates to stabilization components foran implantable blood pump.

Ventricular assist devices, known as VADs, are implantable blood pumpsused for both short-term (i.e., days, months) and long-term applications(i.e., years or a lifetime) where a patient's heart is incapable ofproviding adequate circulation, commonly referred to as heart failure orcongestive heart failure. According to the American Heart Association,more than five million Americans are living with heart failure, withabout 670,000 new cases diagnosed every year. People with heart failureoften have shortness of breath and fatigue. Years of living with blockedarteries or high blood pressure can leave your heart too weak to pumpenough blood to your body. As symptoms worsen, advanced heart failuredevelops.

A patient suffering from heart failure, also called congestive heartfailure, may use a VAD while awaiting a heart transplant or as a longterm destination therapy. In another example, a patient may use a VADwhile recovering from heart surgery. Thus, a VAD can supplement a weakheart (i.e., partial support) or can effectively replace the naturalheart's function. VADs can be implanted in the patient's body andpowered by an electrical power source inside or outside the patient'sbody.

While blood pumps have been effective for patients, further improvementsmay be desirable. For example, increased impeller stabilization in anaxial and/or tilt direction may be beneficial. In particular, increasedtilt and/or axial stabilization of an axial flow blood pump may bebeneficial as such pumps may be more susceptible to tilting and/orwobbling within the blood flow path.

BRIEF SUMMARY

In some aspects, an axial flow mechanical circulatory support system maybe provided. The support system may include a housing having an inlet,an outlet, and an internal wall defining a flow path from the inlet tothe outlet. An impeller may be positioned within the housing flow path.The impeller may include a magnetic member and may include blades forpumping blood in a direction from the inlet to the outlet when theimpeller rotates about an axis of rotation. A stator may be positionedabout the impeller for generating a magnetic field to rotate theimpeller. A bearing may be provided for stabilizing the impeller in anaxial direction. The bearing may include a bearing member for applying abearing force against the impeller in an axial direction from the inlettowards the outlet. The bearing may also include a biasing mechanism forapplying a biasing force against the impeller in an axial directionopposite the bearing member while the impeller is at rest.

Optionally, the biasing force may be greater than the bearing force whenthe impeller is at rest such that the impeller rests against the bearingmember when at rest. The biasing member may apply a passive biasingforce. The bearing member may apply a passive bearing force. In someembodiments, the biasing force may only be applied when the impeller isrotating.

The stator may form a passive magnetic bearing. For example, a drivesignal to the stator may be modified to apply the biasing force on theimpeller. The bearing member may be a chamfer bearing. The bearingmember may be a step bearing. The bearing member may be one or moremagnets around the impeller upstream of an axial center of the impeller.Optionally, the bearing member magnets may include yokes. The biasingmechanism may apply a substantially constant axial force. The impellermay have a magnetic body. Optionally, the stator has windings. In manyembodiments, the inlet and the outlet are axially aligned.

In further aspects, a blood pump may be provided that includes a housingwith an inner wall defining an inlet, an outlet downstream from theinlet, and a blood flow path between the inlet and the outlet. A firstportion of the inner wall may have a first inner dimension thatincreases to a second inner dimension in a downstream direction. Animpeller may be included with a magnetic material. The impeller may bepositioned within the blood flow path downstream of the first portion ofthe inner wall. The impeller may have an outer dimension that is greaterthan the first inner dimension of the inner wall such that the firstportion of the inner wall may prevent the impeller from advancingupstream of the first portion of the inner wall. A motor stator may bepositioned about the blood flow path between the inlet and the outlet.The motor stator, during operation, may be configured to generate amagnetic field for suspending the impeller within the blood flow path.The magnetic field generated by the motor stator may bias the impellerto urge the impeller in an upstream direction toward the first portionof the inner wall so as to stabilize the impeller in an axial direction.

The magnetic field of the motor stator may urge the impeller in theupstream direction and axial hydrodynamic forces between the impellerand the first portion of the inner wall may be configured to provideincreased stabilization of the impeller in an axial direction. The bloodpump may avoid the use of permanent magnets in some embodiments. Inother embodiments, a first permanent magnet may be provided forproducing a first permanent magnetic field urging the impeller in thedownstream direction and a second permanent magnet may be provided forproducing a second permanent magnetic field urging the impeller in theupstream direction. The magnetic fields of the first permanent magnetand the second permanent magnet may be configured to provide increasedstabilization of the impeller in the axial direction. The firstpermanent magnet and the second permanent magnet may be ring magnetspositioned about the blood flow path.

A first conical bearing may extending from the inner wall of the housingand into the blood flow path. The impeller may cooperate with the firstconical bearing to provide increased stabilization of the impeller in atilt direction. The magnetic fields of the first permanent magnet andthe second permanent magnet may be configured to cumulatively urge theimpeller towards the first conical bearing. A yoke may be disposed aboutthe motor stator. The yoke may be configured to increase a magnetic fluxdensity associated with the motor stator. A yoke may be disposed aboutthe first permanent magnet. The yoke may be configured to increase amagnetic flux density associated with the first permanent magnet. A yokemay be disposed about the second permanent magnet. The yoke may beconfigured to increase a magnetic flux density associated with thesecond permanent magnet. The magnetic fields of the first permanentmagnet and the second permanent magnet may be configured to cumulativelyurge the impeller in an upstream direction towards the first portion ofthe inner wall.

A first conical bearing may extend from the inner wall of the housingand into the blood flow path. The impeller may cooperate with the firstconical bearing to provide increased stabilization of the impeller in atilt direction. The impeller may have a hub with a conical upstreamportion configured to cooperate with the first conical bearing toprovide increased stabilization of the impeller in the tilt direction.The impeller may have a hub with a conical downstream portion configuredto cooperate with the first conical bearing to provide increasedstabilization of the impeller in the tilt direction. The impeller mayhave blades extending radially from a hub. The blades may have a beveleddownstream edge configured to cooperate with the first conical bearingto provide increased stabilization of the impeller in the tiltdirection.

In further aspects, a method of operating an blood pump may be provided.The pump may have a housing with an inner wall defining an inlet, anoutlet downstream from the inlet, and a blood flow path between theinlet and the outlet. A first portion of the inner wall may have a firstinner dimension that increases to a second inner dimension in adownstream direction. The pump may further include an impeller having amagnetic material and positioned within the blood flow path downstreamof the first portion of the inner wall. The impeller may have an outerdimension that is greater than the first inner dimension of the innerwall such that the first portion of the inner wall prevents the impellerfrom advancing upstream of the first portion of the inner wall. Themethod may include operating a motor stator positioned about the bloodflow path between the inlet and the outlet to generate a magnetic fieldfor suspending the impeller within the blood flow path. Operating themotor stator to produce a magnetic field configured to bias the impellersuch that the impeller is urged in an upstream direction toward thefirst portion of the inner wall so as to stabilize the impeller in anaxial direction.

A blood pump may be provided with a housing with an inner wall definingan inlet, an outlet downstream from the inlet, and a blood flow pathbetween the inlet and the outlet. An impeller may include a magneticmaterial and may be positioned within the blood flow path. A motorstator may be positioned about the blood flow path between the inlet andthe outlet. The motor stator, during operation, may be configured tosuspend the impeller within the blood flow path. A first permanentmagnet may produce a first permanent magnetic field urging the impellerin the downstream direction. A second permanent magnet may produce asecond permanent magnetic field urging the impeller in the upstreamdirection. The magnetic fields of the first permanent magnet and thesecond permanent magnet may be configured to provide increasedstabilization of the impeller in an axial direction.

The first permanent magnet and the second permanent magnet may be ringmagnets positioned about the blood flow path. A first conical bearingmay extend from the inner wall of the housing and into the blood flowpath. The impeller may cooperate with the first conical bearing toprovide increased stabilization of the impeller in a tilt direction. Theimpeller may have a hub with a conical upstream portion configured tocooperate with the first conical bearing to provide increasedstabilization of the impeller in the tilt direction. The first conicalbearing may comprise a surface angled at 45 degrees relative to an axisof rotation of the impeller to provide tilt and axial hydrodynamicforces. The surface of the conical upstream portion of the hub may angletoward the axis of rotation of the impeller at 45 degrees. The radialand axial hydrodynamic forces between the surface of the first conicalbearing and the surface of the conical upstream portion of the hub mayincrease stabilization of the impeller in the tilt and axial direction.The impeller may have a hub with a conical downstream portion configuredto cooperate with the first conical bearing to provide increasedstabilization of the impeller in the tilt direction. The first conicalbearing may have a surface angled at 45 degrees relative to an axis ofrotation of the impeller to provide radial and axial hydrodynamicforces. A surface of the conical downstream portion of the hub may angletoward the axis of rotation of the impeller at 45 degrees. The radialand axial hydrodynamic forces between the surface of the first conicalbearing and the surface of the conical downstream portion of the hub mayincrease stabilization of the impeller in the tilt and axial direction.

The impeller may include blades extending radially from a hub. Theblades may have beveled upstream edges configured to cooperate with thefirst conical bearing to provide increased stabilization of the impellerin the tilt direction. The first conical bearing may have a surfaceangled at 45 degrees relative to an axis of rotation of the impeller toprovide radial and axial hydrodynamic forces. The blade tips of beveledupstream edges of the blades of the impeller may angle toward the axisof rotation of the impeller at 45 degrees. The radial and axialhydrodynamic forces between the surface of the first conical bearing andblade tips of beveled upstream edges of the blades of the impeller mayincrease stabilization of the impeller in the tilt and axial direction.

A second conical bearing may extend from the inner wall of the housingand into the blood flow path. The second conical bearing may bepositioned downstream from the first conical bearing. An upstreamportion of the impeller may cooperate with the first conical bearing anda downstream portion of the impeller may cooperate with the secondconical bearing to provide increased stabilization of the impeller inthe tilt direction.

Optionally the magnetic fields of the first permanent magnet and thesecond permanent magnet cumulatively urge the impeller towards the firstconical bearing. A yoke may be disposed about the motor stator. The yokemay be configured to increase a magnetic flux density of the motorstator. A yoke may be disposed about the first permanent magnet. Theyoke may be configured to increase a magnetic flux density of the firstpermanent magnet. A yoke may be disposed about the second permanentmagnet. The yoke may be configured to increase a magnetic flux densityof the second permanent magnet.

A first portion of the inner wall may have a first inner dimension thatincreases to a second inner dimension in a downstream direction. Theimpeller may have an outer dimension that is greater than the firstinner dimension of the inner wall such that the first portion of theinner wall prevents the impeller from advancing upstream of the firstportion of the inner wall. The magnetic fields of the first permanentmagnet and the second permanent magnet may cumulatively urge theimpeller in an upstream direction towards the first portion of the innerwall. A magnetic field generated by the motor stator may be configuredto bias the impeller such that the magnetic field of the motor statorurges the impeller in an upstream direction toward the first portion ofthe inner wall.

In further aspects a blood pump may be provided. A housing with an innerwall may define an inlet, an outlet downstream from the inlet, and ablood flow path between the inlet and the outlet. An impeller mayinclude a magnetic material and may be positioned within the blood flowpath. A motor stator may be positioned about the blood flow path betweenthe inlet and the outlet. The motor stator, during operation, may beconfigured to generate a magnetic field for suspending the impellerwithin the blood flow path. A first conical bearing may extend from theinner wall of the housing and into the blood flow path. The impeller maycooperates with the first conical bearing to provide increasedstabilization of the impeller in a tilt direction. The magnetic fieldgenerated by the motor stator may be configured to bias the impellersuch that the magnetic field urges the impeller toward the first conicalbearing so as to stabilize the impeller in an axial direction. Themagnetic field of the motor stator urging the impeller toward the firstconical bearing and axial hydrodynamic forces between the impeller andthe first conical bearing may be configured to provide increasedstabilization of the impeller in an axial direction. The impeller mayhave a hub with a conical upstream portion configured to cooperate withthe first conical bearing to provide increased stabilization of theimpeller in the tilt direction. The impeller may have a hub with aconical downstream portion configured to cooperate with the firstconical bearing to provide increased stabilization of the impeller inthe tilt direction.

The impeller may include blades extending radially from a hub. Theblades may have beveled downstream edges configured to cooperate withthe first conical bearing to provide increased stabilization of theimpeller in the tilt direction.

The blood pump may further include a first permanent magnet producing afirst permanent magnetic field urging the impeller in the downstreamdirection. A second permanent magnet may producing a second permanentmagnetic field urging the impeller in the upstream direction. Themagnetic fields of the first permanent magnet and the second permanentmagnet may be configured to provide increased stabilization of theimpeller in the axial direction. A yoke may be disposed about the motorstator. The yoke may be configured to increase a magnetic flux densityof the motor stator. A yoke may be disposed about the first permanentmagnet. The yoke may be configured to increase a magnetic flux densityof the first permanent magnet. A yoke may be disposed about the secondpermanent magnet. The yoke may be configured to increase a magnetic fluxdensity of the second permanent magnet.

A second conical bearing may extend from the inner wall of the housingand into the blood flow path. The second conical bearing may bepositioned downstream from the first conical bearing. An upstreamportion of the impeller may cooperate with the first conical bearing anda downstream portion of the impeller may cooperate with the secondconical bearing to provide increased stabilization of the impeller inthe tilt direction.

In even further aspects, a blood pump may be provided with a housingwith an inner wall defining an inlet, an outlet downstream from theinlet, and a blood flow path between the inlet and the outlet. A firstportion of the inner wall may have a first inner dimension thatincreases to a second inner dimension in an upstream direction. Animpeller may include a magnetic material and may be positioned withinthe blood flow path upstream of the first portion of the inner wall. Theimpeller may have an outer dimension that is greater than the firstinner dimension of the inner wall such that the first portion of theinner wall prevents the impeller from advancing downstream of the firstportion of the inner wall. A motor stator may be positioned about theblood flow path between the inlet and the outlet. The motor stator,during operation, may be configured to generate a magnetic field forsuspending the impeller within the blood flow path. The magnetic fieldgenerated by the motor stator may be configured to apply a biasing forceon the impeller such that the magnetic field urges the impeller in adownstream direction toward the first portion of the inner wall. Themagnetic field of the motor stator may urge the impeller in thedownstream direction and axial hydrodynamic forces between the impellerand the first portion of the inner wall may be configured to provideincreased stabilization of the impeller in an axial direction.

The terms “invention,” “the invention,” “this invention” and “thepresent invention” used in this patent are intended to refer broadly toall of the subject matter of this patent and the patent claims below.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of thepatent claims below. Embodiments of the invention covered by this patentare defined by the claims below, not this summary. This summary is ahigh-level overview of various aspects of the invention and introducessome of the concepts that are further described in the DetailedDescription section below. This summary is not intended to identify keyor essential features of the claimed subject matter, nor it is intendedto be used in isolation to determine the scope of the claimed subjectmatter. The subject matter should be understood by reference toappropriate portions of the entire specification of this patent, any orall drawings and each claim. The invention will be better understoodupon reading the following description and examining the figures whichaccompany it.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects, and embodiments of the invention will bedescribed by way of example only and with reference to the drawings. Inthe drawings, like reference numbers are used to identify like orfunctionally similar elements. Elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 is an illustration of a mechanical circulatory support systemimplanted in a patient's body.

FIG. 2 illustrates a blood pump with stabilization components accordingto some embodiments of the present invention.

FIG. 3 illustrates another blood pump with stabilization componentsaccording to some embodiments of the present invention.

FIG. 4 illustrates another blood pump that is a modified version of theblood pump illustrated in FIG. 3 according to some embodiments of thepresent invention.

FIG. 5 illustrates yet another blood pump that is another modifiedversion of the blood pump illustrated in FIG. 3 according to someembodiments of the present invention.

FIG. 6 illustrates yet another blood pump with stabilization componentsaccording to some embodiments of the present invention.

FIG. 7 illustrates yet another blood pump with stabilization componentsaccording to some embodiments of the present invention.

FIG. 8 illustrates an exemplary centrifugal pump according to someembodiments of the present invention.

DETAILED DESCRIPTION

FIG. 1 is an illustration of a mechanical circulatory support system 10implanted in a patient's body 12. The mechanical circulatory supportsystem 10 comprises an implantable blood pump 14, outflow cannula 18,system controller 20, and power sources 22. The implantable blood pump14 may comprise a VAD that is attached to an apex of the left ventricle,as illustrated, or the right ventricle, or both ventricles of the heart24. The VAD may comprise a centrifugal or axial flow pump as describedin further detail herein that is capable of pumping the entire outputdelivered to the left ventricle from the pulmonary circulation (i.e., upto 10 liters per minute). Related blood pumps applicable to the presentinvention are described in greater detail below and in U.S. Pat. Nos.5,695,471, 6,071,093, 6,116,862, 6,186,665, 6,234,772, 6,264,635,6,688,861, 7,699,586, 7,976,271, 7,997,854, 8,007,254, 8,152,493,8,419,609, 8,852,072, 8,652,024, 8,668,473, 8,864,643, 8,882,744,9,068,572, 9,091,271, 9,265,870, 9,382,908, all of which areincorporated herein by reference for all purposes in their entirety.With reference to FIGS. 1 and 2, the blood pump 14 may be attached tothe heart 24 via a ventricular cuff which is sewn to the heart 24 andcoupled to the blood pump 14. The other end of the blood pump 14connects to the ascending aorta via the outflow cannula 18 so that theVAD effectively diverts blood from the weakened ventricle and propels itto the aorta for circulation to the rest of the patient's vascularsystem.

FIG. 1 illustrates the mechanical circulatory support system 10 duringbattery 22 powered operation. A driveline 26 which exits through thepatient's abdomen 28, connects the implanted blood pump 14 to the systemcontroller 20, which monitors system 10 operation. Related controllersystems applicable to the present invention are described in greaterdetail below and in U.S. Pat. Nos. 5,888,242, 6,991,595, 8,323,174,8,449,444, 8,506,471, 8,597,350, and 8,657,733 and U.S. PatentPublication Nos. 2005/0071001 and 2013/0314047, all of which areincorporated herein by reference for all purposes in their entirety. Thesystem may be powered by either one, two, or more batteries 22. It willbe appreciated that although the system controller 20 and power source22 are illustrated outside/external to the patient body, the driveline26, system controller 20 and/or power source 22 may be partially orfully implantable within the patient, as separate components orintegrated with the blood bump 14. Examples of such modifications arefurther described in U.S. Pat. Nos. 8,562,508 and 9,079,043, all ofwhich are incorporated herein by reference for all purposes in theirentirety.

Pump 14 may include an impeller suspended in a blood flow path. As theimpeller rotates within the blood flow path about its axis, the impellermay experience forces that can destabilize the impeller within the bloodflow path. These forces may cause: 1) axial destabilization where theimpeller translates in the axial direction from a desired position(e.g., in an upstream or downstream direction), 2) radialdestabilization where the axis of the impeller translates from a desiredposition in a direction perpendicular to the axial direction (e.g.,off-center with the blood flow path or the like), and/or 3) tiltdestabilization where the impeller rotates about a directionperpendicular to the axial direction (e.g., impeller “wobbling”).

FIG. 2 illustrates an exemplary pump 200 according to some embodiments.Blood pump 200 may be configured to assist in pumping blood through apatient's vascular system. The pump 200 may include a housing 202. Thehousing 202 may be non-magnetic and may be made of suitablebiocompatible material such as titanium or a suitable ceramic materialwhich is non-thrombogenic, rigid, and exhibits minimum eddy currentlosses. The housing 202 may define a blood inlet 204, a blood outlet206, and a blood flow path between the inlet 204 and the outlet 206 sothat blood flows through the housing 202 in the direction shown by thearrow 208. In some embodiments, housing 202 may have a constant exteriordiameter while the inlet portion of its interior diameter may firstconverge and thereafter diverge so as to define a constriction 209 inthe blood flow path.

A rotor 210 may be positioned within the blood flow path defined by thehousing 202, and may act as an impeller for pumping fluid along theblood flow path. Rotor 210 may have one or more grooves 212 each ofwhich extends from an entry section or inlet channel 213 at the leadingedge 214 to an exit section or outlet channel 215 at the trailing edge216 of the rotor 210. The grooves 212 define fluid flow channels acrossthe rotor 210. In some embodiments a plurality of grooves 212 formed inthe rotor 210 are spaced apart and define a plurality of blades withblade tips 218 therebetween. Each groove 212 is defined by a pair ofside walls 220 extending substantially radially to the rotational axisof the rotor 210, but not necessarily parallel to each other.

Each of the grooves 212 may have a central flow channel that curves atleast partially around the rotational axis of the rotor 210 and opensinto a substantially axially extending outlet channel 215. The curvedcentral portion may be narrower than the inlet channel 213 or outletchannel 215. The relatively wide outlet channel 215 and its axialorientation may enhance the discharge flow characteristics of the bloodbeing pumped by more easily allowing for the release of blood from therotor 210. The grooves 212 and their side walls 220 may drive blood inthe axial direction, shown by the arrow 208, as the rotor 210 is rotated(clockwise in the embodiment of FIG. 2).

In one embodiment, the number of grooves 212 may be in the range of from2 to 8, with four being typical. Irrespective of the number of grooves212, their collective widths at the periphery of the rotor 210 may beequal to or substantially less than the collective, totalcircumferential width at of the blade tips 218 between the grooves 212.Collectively, the total width of the grooves 212 may be less than orequal to the collective, total width of the respective widths of theblade tip 218.

In this embodiment, the depth of each of the grooves 212 is greater thanthe radial extent of the blades in comparable and conventional thinblade axial pump designs. For example, for heart pump 200 uses theheight of the rotor blades from the axis of rotation of the rotor 210 totheir outer tips 218 may be at least 2 mm, up to typically about 10 mm.Alternatively, the average depth of the grooves 212 from their outerperimeters may fall within the range of from 1 mm to 5 mm. In someembodiments the average depth of the grooves 212 is approximately ⅓ thediameter of the rotor 210, but is less than the radius of the rotor 210.In other embodiments the grooves 212 may be deeper at the entry channel213 at the leading edge 214 of the rotor 210 and shallower at the exitchannel 215 at the trailing edge 216 of the rotor 210.

The blade tips 218 of the rotor 210 are each provided with one or morehydrodynamic thrust bearing surfaces 230. Each of the thrust bearingsurfaces 230 is disposed along the surface of the associated blade tiphaving a prescribed peripheral radius. The leading edge of each of thebearing surfaces 230 from the viewpoint of the (clockwise) spin of therotor 210, is recessed by a predetermined amount below the surface ofthe associated blade tip 218. The recessed surface then tapers in agradual, curved manner across the blade tip 218 along an arc, the axisof curvature of which is not necessarily co-axial with the rotationalaxis of the rotor 210. The tapered bearing surface 230 terminates at arear end, at which point each bearing surface 230 is feathered into theperiphery of the blade tip 218 with a smooth transition and is no longerrecessed with respect to the continuing downstream surface of the landarea.

As the rotor 210 rotates, the respective thrust bearings 230 on eachblade tip 281 scoop blood onto the bearing surfaces 230 whereby it flowsbetween the bearing surfaces and the inner wall of the tubular pumphousing 202. The effect of the tapered configuration of the thrustbearing surfaces 230 is to force blood to flow through a decreasing orconstricting area created between the bearing surfaces 230 and the innerwall of the tubular pump housing 202.

This results in increasing fluid pressure upstream within theconstriction, which pressure acts against the bearing surface areas 230and produces a net symmetrical force for radial support of the spinningrotor 210. The hydrodynamic force that is thus created on the surfacesof the rotor blade tips 218 tends to hold the rotor 210 suspended andcentered within the lumen of the tubular housing 20 in a manner shown inFIG. 2, and resists dynamic, radial shock loading forces without theneed for physically contacting bearing surfaces. The thrust bearingsurfaces 230 may be formed directly into the peripheral surfaces of theblade tips 218 or may be placed within suitable cavities formed in theouter peripheral surfaces of the blade tips 218 and held in place by asuitable cover.

In some embodiments, hydrodynamic thrust bearing surfaces 230 arecreated on the leading 214 or trailing edge portions 216 of the rotor210. For example, with reference to FIG. 2, the bearing 230 at theleading edge 214 of the rotor 210 is tapered or beveled toward the axisof the rotor 210 to cooperate with the constriction 209 of the tubularpump housing 202. Such a thrust bearing 230 would resist longitudinalmovement of the rotor to the left, as shown in FIG. 2 as an outerdimension of the rotor 210 is greater than the dimension of theconstriction 209. Alternatively, the constriction 209 may, if desired,comprise hydrodynamic thrust bearings cooperating with the adjacentrotor surface to prevent contact between the rotor 210 and theconstriction 209 as the rotor 210 rotates.

Hydrodynamic thrust bearing surfaces may also be located on the rotor210 near its trailing edge 216, in which event the inner diameter of thetubular pump housing 202 near its outlet end 206 would be constricted asshown in FIG. 2 to define a constriction 209. Such thrust bearings onthe rotor 210 or formed on a side of the constriction would serve thesimilar purpose of replacing or of supplementing the attractive magneticpoles of magnets 56 and 57 described below. Such thrust bearings mayprovide one or both of radial and axial support for the rotor 210 andserve to increase the resistance to shock loading thereby improvingrotor 210 stability.

Hydrodynamic thrust bearings 230 on the outer periphery of the rotor 210provide good surface washing. Centrifugal forces created by thrustbearings 230 tend to push fluid toward the periphery of the housing 202interior, providing increased blood flow, which can improve the pump'sresistance to thrombosis. Thus, since by this invention, conditions areprovided that reduce blood coagulation, a lower amount of anticoagulantmay be used with the blood pump 200 and patient, which may result infewer patient adverse side effects. If desired, hydrodynamic thrustbearing surfaces 230 may be aligned in a helical fashion on the surfacesof the rotor 210 to improve surface washing by the moving blood as therotor spins.

As an alternative to hydrodynamic thrust bearings 230 acting axially onthe rotor 210, or in addition thereto, permanent rotor retaining magnets222 may be placed in each blade tip 218 within the lead 214, trailing216 or both ends of the rotor 210. One or more corresponding permanentmagnets 232 may be placed within or on the tubular pump housing 202adjacent each rotor retaining magnet 222 to effect attractive magneticforces acting to retain the axial alignment of the rotor 210 within thehousing 202. By way of example only, a permanent magnet 222 is shown inFIG. 2 on a blade tip 218 at the trailing end 216 of the rotor 210. Acorresponding permanent stator magnet 232 is placed within the enclosure228 surrounding the tubular housing 202. The rotor magnet 222 may beformed by magnetizing suitable rotor material. If the north pole of therotor magnet 222 and the south pole of the stator magnet 232 areadjacent or face each other, as shown in FIG. 2, the attracting magneticforces will assist in retaining the rotor 210 in the proper axialposition. Longitudinal or axial movement of the rotor 210 to the rightis thereby restricted by the attractive action of magnets 222 and 232.Of course, magnetic south poles of magnet 222 could be directed to facea north pole of magnet 232 in similar manner, to achieve a generallysimilar effect. It will be understood that the magnet 232 may comprise aring magnet or an electromagnetic coil.

In some embodiments the stator magnet 232 may be placed upstream of thecorresponding magnets 222. As such the magnet 232 may urge the rotor 210upstream toward the upstream constriction 209. While illustrated at thetrailing end 216 of rotor 210, it should be understood that magnets 222may be placed at a leading end 214 and magnets 232 may be positionedaxially upstream from the magnets 222 at the leading end 214 so as toprovide an attracting force on the rotor 210 toward the constriction209. Additionally in some embodiments, the magnets 232 may be positionedwithin the constriction 209 portion of housing 202 to provide theattracting force between the upstream constriction portion 209 and therotor 210.

In further embodiments, the magnet 232 may be placed axially downstreamfrom magnets 222 of rotor 210. An attraction force between the magnets232 and 222 may be configured to urge the rotor 210 toward a downstreamconstriction 209 to provide the axial stabilization. In someembodiments, the magnet 232 may be positioned within the downstreamconstriction 209 to provide the attractive axially stabilizing forcebetween the rotor 210 and the housing 202. Thus in some embodiments,pump 200 may not include an upstream constriction 209 and may rely on adownstream constriction. In some embodiments, rather than usingattracting ends of the magnets 232 and 222, repulsing ends of themagnets 232 and 222 may be used to urge the rotor 210 in a downstreamdirection toward a downstream constriction 209 so as to provide theincreased axial stabilization. In further embodiments, the trailing end216 of the rotor 210 may experience a force opposite that experienced atthe leading end 214 of the rotor 210. For example, the trailing end 216may experience an attractive force with a corresponding stator magnet232, while the leading end 214 may experience a repulsive force with acorresponding stator magnet 232, or vice versa. The cumulative magneticforce on the rotor 210 may be configured to urge the rotor 210 towardthe upstream constriction 209 or towards a downstream constriction 209.In some embodiments, the pump housing may not have any constrictions andmay rely on magnetic forces alone, as will be described further below.

In some embodiments, the rotor 210 may be produced by either machining,molding, or casting a single piece of ferromagnetic material, such ascompression bonded neodymium or Alnico (aluminum-nickel alloy), or analloy of about 70-80 percent by weight of platinum and about 20-30percent by weight of cobalt. In some embodiments, from essentially 76-79percent by weight of platinum is present in the alloy. In someembodiments, the alloy may contain essentially from 21-24 percent byweight of cobalt. In one embodiment, an integral, one-piece rotorconsists of essentially 77.6 percent by weight of platinum and 22.4percent by weight of cobalt. Such a rotor is conventionally heat treatedto achieve good magnetic properties, and may be magnetized, with Northand South magnetic poles, as desired.

The rotor 210 may include a plurality of relatively large permanentdrive magnets formed within each of the blade tips 218 of the rotor 210.According to some embodiments of the present invention, the permanentdrive magnets in the rotor 210 may be produced by magnetizing selectedportions of the peripheries of the blade tips 218. This may beaccomplished, for example, by constructing the rotor 210 from a magneticalloy, which may be isotropic, and magnetizing desired peripheralsections to form a plurality of magnetic poles with various geometricorientations. It is preferable to use a magnetic alloy that isbiocompatible so that no additional coating is required. Such a rotor210 may be easier and less expensive to manufacture than impellersformed from multiple parts.

With reference to FIG. 2, the pump 200 also comprises a motor stator 224having electrically conductive coils 226. The coils 226 are placedwithin an enclosure 228 which surrounds the tubular housing 202 and therotor 210. The motor stator 224 serves to rotate rotor 210 by theconventional application of electric power to the coils 226 to createmagnetic flux. The permanent drive magnets incorporated into the bladetips 218 of the rotor 210 are selected for magnetic properties, length,and cross-sectional area in order to provide good electromagneticcoupling with the magnetic flux created by the motor stator 224. Becauseof the relatively large surface area of the blade tips 218, the natureand placement of the rotor magnets becomes relatively easy to effect.This arrangement provides strong electromagnetic coupling and thenecessary magnetic axial stiffness to maintain the rotor in position. Inone embodiment, the magnetic coupling between the stator flux and thedrive magnets in the rotor 210 creates torque, causing the rotor 210 torotate clockwise. It will be understood by those skilled in the art thatthe rotor 210 could be caused to rotate in a counterclockwise directionwithout departing from the scope of the invention.

The motor 224 may be a three phase, brushless DC motor. In oneembodiment the motor 224 could be a toroidal, three phase and wyeconnected design. The stator 224 may have a back iron design which isconsistent with a typical radial flux gap motor. If desired, the motorstator 224 can comprise a separate, hermetically sealed enclosure 228that slides over the tubular housing 202 into position. A braised weldring to the enclosure 228 outer surface may be used to secure the motorstator housing 228 in position. Laser welding is one possibility forsecuring the motor stator enclosure 228 to the housing 202 and obtaininga hermetic seal.

In some embodiments, a drive signal of the motor stator 226 may beconfigured to bias the rotor 210 toward the constriction 209. In someembodiments, an axial center of the motor stator 226 may be offset froman axial center of the rotor 210. In some embodiments, the axial centerof the motor stator 226 may be upstream relative to the axial center ofthe rotor 210. The offset between the axial centers of the motor stator226 and the rotor 210 may be configured to urge or bias the rotor 210toward the constriction 209 thereby providing increased axialstabilization.

As discussed above, a magnet (e.g., ring magnet or the like) may bepositioned about the blood flow path at a position upstream from therotor to provide an attraction force that urges or biases the rotortoward a constriction. FIG. 3 illustrates an exemplary pump 300 wherethe ring magnet is positioned within the constriction. Pump 300 includesa rotor 310. The rotor 310 is magnetic and biocompatible, and furtherincludes an upstream end 314, a downstream end 316 and an axis Rextending between the ends. The body 310 further includes a plurality ofvanes or blades 311 defining a plurality of channels 320 therebetween.The rotor body 310 is constructed and arranged to impel blooddownstream, in the direction of fluid flow F, upon rotation of the rotorabout axis R in a forward circumferential direction.

Each vane 311 includes at least one hydrodynamic thrust bearing surface330. As further explained below, each thrust bearing surface 330 isconstructed and arranged to apply a hydrodynamic force V (FIG. 3) to therotor 310 with a component of the force in the downstream direction Dupon rotation of the rotor 310 in the clockwise direction (when viewedin the downstream direction). Each vane 311 also has additional radialbearing surfaces 331 along the length of body 310. The radial bearingsurfaces are arranged to apply hydrodynamic forces directed generallyradially inwardly, toward axis R, upon rotation of the rotor 310.

Each thrust bearing surface 330 has a normal vector X. As referred toherein, the normal vector of a surface is the vector directed out of thesurface and perpendicular to the surface. Where the surface isnon-planar, the normal vector of the surface as referred to hereinshould be understood as the integral of the normal vector over theentire extent of the surface. In the embodiment of FIG. 3, the normalvector X of each thrust bearing surface includes non-zero components inthe radially outward direction, in the upstream direction, and in thecircumferentially forward direction. As best seen in FIG. 3, vector Xprojects in the upstream direction U and projects radially outward, awayfrom the axis of rotation R.

Further in this embodiment, the rotor body 310 includes a principalsurface of revolution about the axis R, generally defined as theperipheral surfaces of vanes 311, that is substantially cylindrical inshape. The substantially cylindrical principal surface of revolutiongenerally has an outside diameter, which is preferably about 4 to about12 mm in the case of a blood pump 300 intended for intravascularimplantation in an adult human, and more preferably about 9 to 11 mm.Vanes 311 define chamfer or beveled surfaces 313 at the upstream ends ofthe vanes 311. The chamfer surfaces 313 slope radially outwardly in thedownstream direction, so that the chamfer surfaces 313 are generally inthe form of portions of a conical surface of revolution about the axishaving increasing diameter in the downstream direction. As illustratedin FIG. 3, the downstream diameter of the chamfer surfaces 313 may besubstantially equal to the first diameter of the vanes 311 and thecylindrical surface of revolution of body 310. Thrust bearing surfaces330 are provided as portions of the chamfer surfaces 313. Thrust bearingsurfaces 330 are recessed relative to surrounding portions of thechamfer surfaces 313 such that each thrust bearing surface 330 defines apocket in the chamfer surfaces 313. Each pocket, defining thrust bearingsurface 313, includes a leading portion 338 and a trailing portion 340in the rotation direction. The pocket has a progressively increasingdepth such that the deepest portion of the pocket is at leading portion.Stated another way, each thrust bearing surface 330 slopes progressivelyoutward, toward the surrounding chamfer surface 313, in the directionfrom the leading portion to the trailing portion. Moreover, the leadingportion is open to adjacent channel 320. The difference between thethrust bearing surface 330 at leading portion and the chamfered surface313, measured adjacent to leading portion, defines a radial gap height,which may be within the range of about 0.0010 inches to about 0.0020inches, such as, for example, 0.0010 inches, 0.0015 inches, 0.0020inches, or the like.

The chamfer surfaces 313 define a chamfer angle A such that the chamfersurfaces 313 are positioned at an angle relative to axis R and relativethe generally cylindrical surface of revolution of the rotor body 310.Chamfer angle desirably is in the range of about 20 degrees to about 45degrees, and typically is less than 45 degrees. For example, the chamferangle A of the chamfer surfaces 313 may be about 30 degrees. The chamfersurfaces 313 have a chamfer length L measured in the axial directionswhich may be in the range of about 0.06 inches (1.5 mm) to about 0.1inches (2.5 mm). In one example, the chamfer length L is about 0.08inches (2 mm).

The rotor body 310 may further include and projection members 334 and336 extending upstream and downstream from the vanes 311. The particularexample of the rotor 300 shown in FIG. 3 includes four vanes 311defining four channels 320, each vane 311 having two radial bearings 331on the blade tips of the vanes 311 defining the cylindrical surface ofrevolution of body 310. Each radial bearing 331 is formed as a recessedpocket in the peripheral surface of the vane 311, and each such pockethas its maximum depth at the leading edge of the pocket, i.e., the edgeof the pocket which lies at the circumferentially forward side. Thedepth of each pocket 331 decreases progressively toward the trailing endof the pocket 331. The radial bearing pockets 331 are open to channels320 at the leading edges of the pockets 331. Any number of vanes 311 andradial bearings 331 is contemplated.

Rotor body 310 is positioned within a hollow casing 302. The hollowcasing 302 defines flow path therethrough, within which the rotor body310 is positioned. Casing 302 also includes an upstream end and adownstream end, corresponding to the direction of fluid flow F, andcorresponding to the upstream and downstream ends of the rotor 310. Theflow path has a central axis R coincident with the central axis of therotor 310, an inlet 304 at its upstream end and an outlet 306 at itsdownstream end. Casing 302 further includes a mechanical stop surface309 positioned upstream of vanes 311 and chamfer surfaces 313 of rotorbody 310. The stop surface 309 is intended to prohibit excessiveupstream motion of the rotor body 310 out of its ordinary position.

As shown in FIG. 3, the stop surface 309 is positioned adjacent to aportion of the rotor body 310 and may be shaped similarly to suchportion of body 310. In this embodiment, the stop surface 309 issubstantially in the form of a surface of revolution about the centralaxis R, such surface facing inwardly toward the central axis. The stopsurface 309 has a diameter increasing progressively in the downstreamdirection. In this embodiment, the stop surface 309 is substantiallyconical, and lies at an angle A to the central axis which issubstantially equal to the angle A of the chamfer surfaces 313. The stopsurface 309 may have a length in the axial direction approximately equalto the length L of the chamfer surfaces 313. The smaller (minor) insidediameter of the stop surface 309 should be less than the outsidediameter defined by the vanes 311. The main portion of the flow path305, downstream from stop surface 309, desirably has an inside diameterjust slightly larger than the outside diameter OD defined by the vanes311 on the rotor 310.

The casing 302 may include additional features such as a downstream stop(not shown) to prevent movement of the rotor out of the casing throughthe outlet 306 while the pump 300 is inactive. Also, a set of stationaryvanes, sometimes referred to as a “diffuser” (not shown) may bepositioned downstream from the rotor 310. The vanes of the diffuser maybe arranged to reduce rotation of fluid around the axis R.

A motor stator 324 is disposed in proximity to casing 302 and outside ofthe flow path and preferably surrounding at least a portion of the rotorbody 310. The stator 324 may include one or more electromagnetic coils,most commonly a plurality of coils such as three coils disposed at equal120 degree intervals about the central axis R, as discussed above and asis known in the art. In operation, a power source (not shown) createsalternating currents which pass through the coils, to create a magneticfield in a direction transverse to axis R and rotating axis R. Thisfield is applied to the rotor so as to rotate the rotor body 310 aboutaxis R. The magnetic field of the stator also tends to hold the rotor inposition along the axis, in alignment with the stator. As discussedabove, this effect is referred to as the axial magnetic stiffness of thestator.

Casing 302 may be made of any non-ferromagnetic material capable ofhandling the rotor 310 operation, which substantially resiststhrombosis, and which is biocompatible. Desirably, the casing materialshould be resistant to mechanical wear. For example, the material ofcasing 302 may be a ceramic. Rotor body 310 includes a magnetically hardferromagnetic material, i.e., a material which forms a strong permanentmagnet and which is resistant to demagnetization. The material of therotor body also should be biocompatible and substantiallynon-thrombogenic. For example, the rotor body may be formed as a unitarymass of an alloy of platinum and cobalt. In other embodiments, the rotorbody may be formed from a magnetic metal such as an iron-nickel alloywith an exterior coating of another material to increase the body'sbiocompatibility. The rotor is magnetized with a magnetic fieldtransverse to the axis R, so as to provide magnetic poles at theperipheral surfaces of the vanes.

In operation, the stator 324 is actuated by the power source to providea rotating magnetic field and thus spin the rotor 310 about axis R. Asthe rotor 310 spins, the radial bearings 331 hold the rotor 310 centeredwithin the flow path of the housing 302 and out of contact with the wall302. The radial bearings 331 operate as hydrodynamic bearings. A smallportion of the blood passing through the pump 300 enters the pockets ofthe radial bearings 331, and encounters the sloping pocket surfaces.This interaction generates forces on the rotor 310 directed radiallyinwardly, toward the axis.

A small portion of the blood flowing within the flow path passes betweenthe chamfer surfaces 313 of the rotor 310 and the stop surface 309 ofthe casing 302. This blood enters into the pockets defined by thrustbearing surfaces 330. The thrust bearings also operate as hydrodynamicbearings. As the rotor 310 turns, the blood contained in the pocketsapplies forces to the thrust bearing surfaces 330. These forces aredirected approximately normal to the bearing surfaces. Thus, the forcesare directed along vector V, approximately opposite to the normal vectorX of each thrust bearing surface. The forces on the thrust bearingsurfaces 330 thus have components directed radially inwardly, towardaxis R, and also have components directed in the downstream direction D.

In some embodiments, a stator magnet 332 may be positioned in the stopsurface 309. The stator magnet 332 may have an attraction force betweena corresponding magnet 322 or magnets 322 of the rotor 310. Theattraction force between the stator magnet 332 and the rotor magnets 322may counteract the thrust bearing force from the interaction betweensurface 313 and the stop surface 309 and may maintain the rotor 310 in apreferred position within the flow path. The rotor magnets 322 may bepositioned in the upstream portion 334 or may reside in chamfer surface330, or along the main body of rotor 310.

Alternatively, the stator magnet 332 may be used to provide a repellingforce between a corresponding magnet 322 of the rotor 310. This may beparticularly useful when operating the pump 300 at higher speeds and/orcapacity. The repelling forces between stator magnet 332 may also allowthe pump 300 to be operated at higher rotational speeds than acomparable pump without the repelling magnets 332, 322, to provide agreater pressure differential, greater flow rate or both. In someembodiments, the magnets 332 may be actively controlled to adjust themagnetic forces as impeller speeds change or as the gap between thebearing 309 and the rotor 310 change.

While the pump 200 illustrated in FIG. 2 and the pump 300 illustrated inFIG. 3 include a constriction 209, 309 respectively to provide increasedaxial (translation along the Z-axis) and/or tilt stabilization (rotationoff of the Z-axis), it should be understood that other embodiments mayavoid the use of a constriction in the upstream or downstreamdirections. For example, FIG. 4 illustrates exemplary pump 400.Exemplary pump 400 is a modified version of pump 300 of FIG. 3. Asillustrated, pump 400 may include similar features as pump 300, howeverhousing 402 of pump 400 may not define an upstream constriction portion309 of the flow path to provide for axial and tilt stabilization of therotor 310. Pump 400 may utilize permanent magnets 432 positionedupstream from an axial center of the rotor 320 to provide axialstabilization of the rotor 320 within the flow path. Additionally oralternatively, the pump 400 may utilize permanent magnets 433 positioneddownstream from an axial center of the rotor 320 to provide axialstabilization of the rotor 320 in the flow path. For example, theupstream magnets 432 may provide a repulsion force against the rotor 310as the rotor 310 is in operation to urge the motor 310 in a downstreamdirection and the downstream magnets 433 may provide a repulsion forceagainst the rotor 310 to urge the motor 310 in an upstream direction. Insome embodiments, if forces acting on the rotor 310 at higher operatingspeeds tend to urge the rotor 310 in an upstream direction, magnets 433may provide an attractive force on the rotor 310 to urge the rotor 310in the downstream direction and to counter the forces at the higherspeeds.

Moreover, in some embodiments, as illustrated in FIG. 4, the motorstator of the pump 400 may have two separate components 424 a and 424 b.Motor stator 424 a may be generally positioned about the downstreamportion of the rotor 320 and motor stator 424 b may be generallypositioned about the upstream portion of the rotor 320. Both motorstators 424 a, 424 b may act in concert to drive rotor 320 of pump 400.Additionally, each motor stator 424 a, 424 b may provide additionalaxial stiffness to stabilize the rotor 320 in the axial direction withinthe flow path. Moreover, the motor stator 424 a may provide additionaltilt stabilization of the rotor 320 as it is positioned generally abouta downstream portion of the rotor 320 while motor stator 424 b mayprovide additional tilt stabilization of the rotor 320 as it ispositioned generally about an upstream portion of the rotor 320.

Thus in some embodiments, a pump 400 may be provided without aconstriction (e.g., constriction 209, 309) in the flow path. The pumpmay provide axial and tilt stabilization through the use of one of or acombination of: active control of a plurality of motor stators that areoffset a distance from an axial center of the rotor, magnets 432positioned upstream of the rotor 310, and/or magnets 433 positioneddownstream of the rotor 310.

FIG. 5 illustrates another exemplary pump 500 according to someembodiments of the invention. Exemplary pump 500 is a modified versionof pump 300 of FIG. 3. Pump 500 may have a housing 502 defining a flowpath from the inlet 304 to the outlet 305. The flow path may include astep bearing 509 upstream from the rotor 310. The step bearing may takethe place of the constriction 309 and may provide axial stabilization ofthe rotor 310 within the flow path. Additionally, step bearings 309 maybe positioned downstream of the rotor 310 to provide axial stabilizationin the downstream direction. The step bearings 509 may have hydrodynamicbearing surfaces or may provide a surface where hydrodynamic bearings ofthe rotor 310 interact to provide the axial stabilization forces for therotor 310. While not illustrated, it should be appreciated thatdownstream end 316 of rotor 310 may include a hydrodynamic bearingsurface that cooperates with the downstream step bearings 509 to provideaxial stabilization. Pump 500 may also utilize a two part motor stator424 a, 424 b similar to pump 400. As discussed above, the two part motorstator 424 a, 424 b may be positioned on opposite sides of an axialcenter of the rotor 310 or may otherwise drive opposite ends of therotor 310. In addition to providing axial stabilization, the motorstators 424 a, 424 b may provide additional tilt stabilization for therotor 310 so as to reduce wobbling of the rotor 310 during operation.Further at different pump speeds, the motor stators 424 a, 424 b may becontrolled to bias the rotor 310 in the upstream or downstream directionas needed so as to maintain the rotor 310 at a desired axial position.

A pump according to a further embodiment of the invention includes arotor body 610 (FIG. 6) positioned within a casing 650. In thisembodiment, the vanes or blades of the rotor 610 flare radiallyoutwardly and define chamfer surfaces 630 near the downstream end 624 ofrotor body 610 rather than at the upstream end 623. In this embodiment,the body 610 includes a substantially cylindrical body, but has aportion having a first diameter and a portion having a second diameter.The two portions are separated by the chamfer surfaces 630. Chamfersurfaces 630 are provided with thrust bearing surfaces 635, similar tothrust bearing surfaces of the embodiments discussed above. Casing 650includes stop surface 656, which in this example is positioneddownstream of the stator 652. Here again, the stop surface 656 has aform of at least a portion of a surface of revolution about axis R. Thissurface has a diameter which increases progressively in the downstreamdirection along the bore axis R. Pump 600 operates in a similar fashionas the pumps discussed above. Here again, rotor body 620 is preventedfrom migrating upstream by combined action of the magnet stiffness ofstator 652 and the force generated by thrust surfaces 635.

Optionally, to provide further axial stabilization, upstream and/ordownstream conical bearings 609 may be provided to cooperate with thefront portion 638 and/or back portion 640 of rotor 610. Conical bearings609 may extend from the housing 650 and into the flow channel. Theconical bearings 609 may form a conical opening for cooperating with theupstream and or downstream portions. The conical bearings 609 mayprovide additional axial and tilt stabilization of the rotor 610 duringoperation. Additionally, or alternatively, upstream permanent magnets642 and/or downstream magnets 644 may be provided to bias the rotor 610in the upstream and/or downstream directions for axial stabilization ofthe rotor 610. In some embodiments, it may be preferable if the upstreammagnets 642 are configured to bias the rotor 610 to urge it in adownstream direction. Magnets 644 may be configured to provide either abiasing force in the upstream direction or in the downstream direction.The biasing force provided by downstream magnets 644 may depend on athrust bearing 635 configuration and/or a pump speed. In someembodiments, the magnets 644 may be actively controlled to adjust themagnetic forces as impeller speeds change or as a gap between surface630 and surface 656 change. Additionally, it should be appreciated thatthe attractive/repulsive forces by magnets 642 and 644 may be adjustedby adjusting a distance between the magnets 642, 644 and the rotor 610.

In some embodiments it may be preferable to provide a higher attractiveforce on the upstream end and a less attractive force or a repulsiveforce on the downstream end, such a configuration may provide additionaltilt stabilization. As discussed above, the higher attractive force onthe upstream end may be controlled actively, may be provided by a largermagnet, and/or may be provided by a shorter distance between theupstream magnet 642 and the rotor 610 relative to a distance between thedownstream magnet 644 and the rotor 610.

Additionally, or alternatively, a second motor stator 653 may beprovided about the downstream portion 624 of the rotor 610. The secondmotor stator 653 may also be driven to rotate the rotor 610 in the bloodflow path. Further, the second motor stator 653 may provide additionaltilt stabilization of the downstream portion 624 while the motor stator652 may provide tilt stabilization of the upstream portion 623.

In some embodiments, a yoke 654 may contact the stators 652 and increasethe EMF output to provide additional axial stiffness. For example, insome embodiments, the yoke 654 may be a ring of iron or Permalloy™material above and/or below the stators 652. While illustrated with ayoke 654 on stator 652, it may be beneficial to provide yoke 654 onmagnets 642, stator 653, and/or magnet 644 to increase a magnetic fluxdensity associated with the magnet. It should also be appreciated theyokes 654 may be utilized in combination with other magnets of the aboveembodiments to increase a magnetic flux density of the magnets as neededto provide additional axial and/or tilt stabilization.

FIG. 7 illustrates yet another embodiment of a blood circulating pump700. In this embodiment, the vanes or blades of the rotor 710progressively increase in diameter along the length of the body. Thus,the main portion of rotor body 710 has a tapered peripheral surface 721generally in the form of a surface of revolution about axis R havingprogressively increasing diameter in the downstream direction. In theparticular embodiment depicted, the peripheral surface 721 of the rotormain portion is a cone having a generatrix disposed at an angle A toaxis R. This peripheral surface is provided with bearing surfaces 735.The casing 750 includes a bore with an interior surface 756 which alsohas a diameter which increases progressively in the downstream directionalong the axis R. The inwardly facing surface 756 is complementary tothe outwardly facing peripheral surface 721 of the rotor 710. Thus,surface 756 may be a conical surface having a generatrix disposed atapproximately the same angle A to axis R. Also in this example, thestator 752 surrounds at least a portion of the interior surface 756 andtapered peripheral surface 721 of the rotor. In this embodiment, eachbearing surface 735 has a normal vector X with a positive, non-zerocomponent in the upstream direction U and also in the radially outwarddirection, away from axis R. The normal vector X desirably also has acomponent in the circumferentially forward direction. Upon rotation ofrotor 710 about axis R in the forward direction, each bearing surface735 will be subjected to forces directed along vector V, with bothdownstream and radially inward components. Thus, bearing surfaces 735act as radial bearings to keep the rotor 710 centered in the bore of thehousing 750, and also act as thrust bearing surfaces to providedownstream forces on the rotor. The angle A may be relatively small as,for example, a few degrees while still providing sufficient downstreamforce component.

To provide additional axial stabilization, conical bearings 709 may beprovided upstream and/or downstream of rotor 710. The conical bearings709 may extend into the blood flow path from the housing 750 and maycooperate with the front end 738 and/or the back end 740 to provideincreased axial stabilization of the rotor 710 in the blood flow path.

Additionally, or alternatively, similar to the embodiments describedabove, stator magnets 742 and/or magnets 744 may be provided upstreamand/or downstream from the rotor 710 and may be configured to bias orurge the rotor 710 toward a preferred axial position. The magnets 742,744 may be configured to counter axial forces in the upstream and/ordownstream direction so as to maintain the rotor 710 in a preferredposition. For example, in some embodiments, the magnets 744 may beconfigured to urge the rotor 710 upstream toward the surface 756. Insome embodiments, when the rotor 710 is at rest, the rotor 710 will restagainst surface 756. However, during operation, due to hydrodynamicforces of bearings 735, the rotor 710 may be preferably spaced apartfrom wall 756. In some embodiments, the magnets 742 may also beconfigured to urge the rotor 710 in the upstream direction towardsurface 756. This may be beneficial for preimplantation of the pump 700such that the rotor 710 does not shift within housing 750 duringimplantation. In some embodiments, when rotor 710 experiences increasedforces in the upstream direction, magnets 742 and/or magnets 744 may beconfigured to counter the upstream forces so that the rotor 710maintains a preferred position within housing 750. In some embodiments,the magnets 742,744 may be configured to provide opposing forcesrelative to one another. For example, magnets 742 may be configured tourge the rotor 710 in the downstream direction while magnets 744 may beconfigured to urge the rotor 710 in the upstream direction. As discussedabove, one or more yokes may be applied to the magnets and or motorstator of pump 700 to increase a magnetic flux associated with themagnet and/or motor stator.

Optionally, similar to embodiments described above, in addition or inthe alternative to motor stator 752 may be configured to rotate therotor 710 and to bias the rotor 710 in a direction toward the bearingsurface 756.

In alternative embodiments, the stabilization device described above maybe used in centrifugal pumps. In the centrifugal pumps, the rotors areshaped to accelerate the blood circumferentially and thereby cause it tomove toward the outer rim of the pump, whereas in the axial flow pumpsthe rotors are more or less cylindrical with blades that are helical,causing the blood to be accelerated in the direction of the rotor'saxis. FIG. 8 illustrates an exemplary centrifugal pump 800 according tosome embodiments. This exploded view illustrates three main assembliesthat makeup the rotary blood pump 800: the pump housing assembly 801, amotor assembly 803 and the rotor assembly 805.

Generally speaking, the pump housing assembly 801 makes up the main bodyof the rotary blood pump 800, including a housing top 802 and a housingbottom 804 which fastens by welding and aligned by alignment pins 812 toa top and bottom side of a housing middle 806

As seen in FIG. 8, the rotor assembly 805 is not physically connected tothe housing assembly 801. Instead, the rotor assembly 805 is supportedby an axial hydrodynamic bearing created between a thrust plate 814 anda bottom surface of the rotor assembly 805, a radial hydrodynamicbearing between the inside diameter of the rotor assembly 805 and theoutside diameter of the spindle portion of the thrust plate 814(additionally, or in the alternative, between the outside of the rotorassembly 805 and the inside diameter of the housing assembly 801), andby an axial magnetic bearing created between a spindle magnet 819 and arotor axial magnet 824. The nature of these bearings is discussed indetail in U.S. Pat. No. 7,431,688, entitled Rotary Blood Pump, which isincorporated herein by reference. In some embodiments, one or more ofthe stabilization devices discussed above may be utilized with thecentrifugal pump 800 to provide additional axial, radial, and tiltstabilization. For example, cooperating chamfer surfaces may be providedbetween the outer surface of spindle portion of the thrust plate and theinside diameter of the rotor assembly. Additionally or alternatively, acooperating chamfer surfaces may be provided between the outside surfaceof the rotor assembly 805 and the inner surface of housing assembly 801(e.g., inside surface of middle portion 806). Alternatively, one or morepermanent magnets may be provided to urge the rotor 805 in the upstreamdirection (or alternatively in the downstream direction). Thus, duringoperation, contact between the rotor assembly 805 and the housingassembly 801 are minimized and, in one embodiment, even reduced to zerocontact, thereby reducing friction, minimizing heat generation, anddecreasing power requirements over prior art designs.

U.S. Pat. Nos. 5,695,471, 8,672,611, and 9,512,852 illustratealternative centrifugal pumps which may benefit from stabilizationfeatures described herein, each of the disclosures of which areincorporated herein by reference.

In the foregoing specification, the invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the invention is not limited thereto. Variousfeatures and aspects of the above-described invention can be usedindividually or jointly. Further, the invention can be utilized in anynumber of environments and applications beyond those described hereinwithout departing from the broader spirit and scope of thespecification. The specification and drawings are, accordingly, to beregarded as illustrative rather than restrictive. It will be recognizedthat the terms “comprising,” “including,” and “having,” as used herein,are specifically intended to be read as open-ended terms of art.

What is claimed is:
 1. A blood pump comprising: a housing with an innerwall defining an inlet, an outlet downstream from the inlet, and a bloodflow path between the inlet and the outlet; an impeller comprising amagnetic material positioned within the blood flow path; a motor statorpositioned about the blood flow path between the inlet and the outlet,the motor stator, during operation, configured to generate a magneticfield for suspending the impeller within the blood flow path; a firsttapered bearing extending from the inner wall of the housing and intothe blood flow path, wherein the wherein a tapered portion of theimpeller cooperates with the first tapered bearing to provide increasedstabilization of the impeller in a tilt direction; wherein the magneticfield urges the impeller toward the first tapered bearing so as tostabilize the impeller in an axial direction.
 2. The blood pump of claim1, wherein the magnetic field of the motor stator urging the impellertoward the first tapered bearing and axial hydrodynamic forces betweenthe impeller and the first tapered bearing are configured to provideincreased stabilization of the impeller in the axial direction.
 3. Theblood pump of claim 1, wherein the impeller has a hub with a conicalupstream portion configured to cooperate with the first tapered bearingto provide increased stabilization of the impeller in the tiltdirection.
 4. The blood pump of claim 1, wherein the tapered bearing isconical in shape.
 5. The blood pump of claim 1, wherein the impeller hasa hub with a conical downstream portion configured to cooperate with thefirst tapered bearing to provide increased stabilization of the impellerin the tilt direction.
 6. The blood pump of claim 1, wherein theimpeller further comprises blades extending radially from a hub, theblades comprising beveled downstream edges configured to cooperate withthe first tapered bearing to provide increased stabilization of theimpeller in the tilt direction.
 7. The blood pump of claim 1, furthercomprising: a first permanent magnet producing a first permanentmagnetic field urging the impeller in a direction along a flow directionof the blood flow path; and a second permanent magnet producing a secondpermanent magnetic field urging the impeller in a direction opposite aflow direction of the blood flow path; wherein the first and secondpermanent magnetic fields of the first permanent magnet and the secondpermanent magnet are configured to provide further increasedstabilization of the impeller in the axial direction.
 8. The blood pumpof claim 7, further comprising a yoke disposed about the motor stator,the yoke configured to increase a magnetic flux density of the motorstator.
 9. The blood pump of claim 7, further comprising a yoke disposedabout the first permanent magnet, the yoke configured to increase amagnetic flux density of the first permanent magnet.
 10. The blood pumpof claim 7, further comprising a yoke disposed about the secondpermanent magnet, the yoke configured to increase a magnetic fluxdensity of the second permanent magnet.
 11. The blood pump of claim 1,further comprising a second tapered bearing extending from the innerwall of the housing and into the blood flow path, the second taperedbearing positioned downstream from the first tapered bearing; andwherein an upstream portion of the impeller cooperates with the firsttapered bearing and a downstream portion of the impeller cooperates withthe second tapered bearing to provide increased stabilization of theimpeller in the tilt direction.
 12. The blood pump of claim 1, whereinthe axial direction is along a flow direction of the blood flow path.13. The blood pump of claim 1, wherein the axial direction is opposite aflow direction of the blood flow path.
 14. A method of operating a bloodpump having a housing with an inner wall defining an inlet, an outletdownstream from the inlet, an impeller, a blood flow path between theinlet and the outlet, and a first tapered bearing extending from theinner wall of the housing and into the blood flow path, the methodcomprising: operating a motor stator positioned about the blood flowpath between the inlet and the outlet to generate a magnetic field forsuspending the impeller within the blood flow path, wherein the magneticfield urges the impeller toward the first tapered bearing so as tostabilize the impeller in an axial direction; causing a first taperedportion of the impeller to cooperate with the first tapered bearing toprovide increased stabilization of the impeller in a tilt direction. 15.The method of claim 14, wherein the blood pump further comprises asecond tapered bearing extending from the inner wall of the housing andinto the blood flow path, the method further comprising causing a secondtapered portion of the impeller to cooperate with the second taperedbearing to provide further increased stabilization of the impeller inthe tilt direction.
 16. The method of claim 14, wherein the impellerfurther comprises blades extending radially from a hub, the bladescomprising beveled downstream edges configured to cooperate with thefirst tapered bearing to provide increased stabilization of the impellerin the tilt direction.
 17. The blood pump of claim 14, furthercomprising: producing, by a first permanent magnet, a first permanentmagnetic field urging the impeller in a direction along a flow directionof the blood flow path; and producing, by a second permanent magnet, asecond permanent magnetic field urging the impeller in a directionopposite a flow direction of the blood flow path; wherein the first andsecond permanent magnetic fields of the first permanent magnet and thesecond permanent magnet are configured to provide further increasedstabilization of the impeller in the axial direction.
 18. The method ofclaim 17, wherein the blood pump further comprises a yoke disposed aboutthe motor stator, the method further comprising: increasing, by theyoke, a magnetic flux density of the motor stator.
 19. The method ofclaim 17, wherein the blood pump further comprises a yoke disposed aboutthe first permanent magnet, the method further comprising: increasing,by the yoke, a magnetic flux density of the first permanent magnet. 20.The method of claim 17, wherein the blood pump further comprises a yokedisposed about the second permanent magnet, the method furthercomprising: increasing, by the yoke, a magnetic flux density of thesecond permanent magnet.